Thread cutting equipment for sewing machines



THREAD CUTTING EQUIPMENT FOR SEWING MACHINES Filed Feb. 24, 1964 T- HARRIS Feb. '15, 1966 3 Sheets-Sheet 1 Feb. 15, 1966 T. HAR IS 3,234,900

THREAD CUTTING EQUIPMENT FOR SEWING MACHINES Filed Feb. 24, 1964 v 5 Sheets-Sheet 2 R i; v ,L a: I

' #L s .m 1 2 LR Feb. 15, 1966 HARRls 3,234,900

THREAD CUTTING EQUIPMENT FOR SEWING MACHINES Filed Feb. 24, 1964 3 Sheets-Sheet 5 United States Patent Ofilice 3,234,900 Patented Feb. 15, 1966 3,234,900 THREAD CUTTING EQUIPMENT FOR SEWING MACHINES Thomas Harris, Birstall, Leicester, England, assiguor to Corah-matic Limited, Canning Place, Leicester, England, a British company Filed Feb. 24, 1964, Ser. No. 346,926 Claims priority, application Great Britain, Mar. 2, 1963, 8,438/ 63 4 Claims. (Cl. 112-252) This invention relates to sewing machines and particularly to lockstitch type sewing machines in which independent threads are fed to and are interstitched at the stitching zone. In current forms of these machines there is one thread at the top and one at the bottom, that is to say the threads are presented from above and below the stitch plate in making each stitch in the work. Although we refer above to one top thread and one bottom thread, it will be apprepriated that these are sometimes duplicated, as in the case of a so-called double lockstitch machine, and such duplicate-system machines are to be regarded as falling within the general purview of this invention.

It is an object of the invention to prescribe an inexpensive equipment which can be applied without difficulty to lockstitch machines of the various standard types in current use, and for the purpose of cutting the threads in a simple and efiective fashion.

To this end the equipment referred to comprises a first cutter mounted above the stitch plate of the machine and pivotable to act on the top thread, a second cutter pivotable below this plate for action on the bottom thread, and a mechanical level and linkage system for operating each of said cutters, these two systems being coupled for movement by a single manually-operable lever to implement pivotal movement of both cutters in performance performance of a thread-cutting operation.

Equipment of this character can be made positively acting, can easily be set and adjusted, and can readily be applied to existing lockstitch sewing machines.

In a preferred form, the first and second cutters are knives and are operable by lever and linkage systems respectively disposed above and below the base plate of the machine, and operable in common from a finger lever on the cantilever arm of the machine which carries the stitching head.

This arrangement allows a further feature of the invention to be exploited, namely the provision made for quick setting of the stroke of the top and bottom cutters or knives when the equipment is being initially assembled in the machine or during use. Because of the intercoupling there need only be one setting control serving both mechanisms, and an example of this arrangement will be described later. By the same token one means, conveniently a spring, can be used to cater for resetting of the knives to their starting positions after a thread-cutting operation.

A specific form of the equipment according to this invention, is shown applied to a sewing machine in the accompanying drawing, in which:

FIGURE 1 is a rear view of part of the equipment located above the base plate of the machine.

FIGURE 2 is a plan view corresponding to FIGURE 1.

FIGURE 3 is a plan view from below of the base plate of the machine showing the parts of the equipment disposed below this plate, and

FIGURE 4 is an enlarged end view of the stitching zone of the machine, taken on the line IVIV of FIGURE 1.

In the accompanying drawings the major part of the sewing machine has been illustrated in diagrammatic outline, where it is seen to comprise a base plate 1 with an upstanding post 2 and a cantilever arm 3 which carries the sewing head 4. Depending from the latter is a needle bar 5 which carries the needle 6 and is reciprocated up and down by a conventional mechanism housed within the arm 3 and post 2. This mechanism, which may be of any standard form, has not been illustrated, as it forms no part of the present invention. Similarly the drawings diagrammatically illustrate a shuttle 7 disposed in the usual way beneath the stitch plate 8 of the machine and driven by conventional means which have also not been shown.

The top thread which is introduced by the needle 6 has been designated 9 in FIGURE 4 and is fed from a supply means diagrammatically illustrated at 46 and the bottom thread from the shutter is indicated as 10, these threads being interlooped during the stitching operation in the usual way.

The machine further is shown as having a standard form of presser foot 11 with the usual forked portion 12 for the passage of needle 6.

The top cutter of the equipment in this embodiment of the invention comprises a curved knife blade 13 which is pivoted at 14 to the presser foot 11 and is arcuately reciprocable over the top stitch plate 8. Attached to the blade 13 is a rearwardly directed and cranked arm 15, the outer edge of which is received in. a lever 16 which is pivotable on the stem 17 of the presser foot 11. At its upper end, a lever 16 has a pin 18 received in the forked end of a link 19 which is reciprocable horizontally of the machine, the pin 18 and the forked end providing a lostmotion coupling to allow for raising and lowering of the presser foot. This link is mounted on the end of a bar 20 movable in spaced bearing collars 22 forming part of a bracket 21 depending from the cantilever arm 3 of the machine. At its opposite end the bar 20 carries an arm 23 with a downturned end pin 24 received in a slot in a pivotable arm 25, itself carried by a rotatable stem 26 in a fixed sleeve bearing 27 and passing through the base plate 1 of the machine. The parts 15-26 described above represent the lever and linkage system for operating the first or top cutter 13.

The second or bottom cutter is represented. by an angled knife blade 28 which is pivotable at 31 below the base plate and has mounted thereon a thread positioning finger 23 which has a lead over the cutting edge of the blade.

The lever and linkage system for operating this cutter comprises an arm 32 in the form of a rod bent to form an upstanding swan neck 33 and welded to a plate 34 pivoted at 35 to the body of the machine. The arm 32 has a cranked end portion 36 which is pivotally attached to a lever 37 which runs horizontally below the base plate and is pivoted at 39 to a link 38 secured to the depending lower end of stem 26. By virtue of this coupling, the upper and lower lever and linkage systems are thus arranged for movement in harmony, and such movement is produced by manual operation of a finger piece 40 disposed at the upper and outer end of the cantilever arm 3. This lever is attached to a stem 41 to a linkage 42, 43 coupled to the links 37 and 38 at pivot 39, so that a simple flick of finger piece 40 will produce simultaneous operation of both cutter knives and a trapping of the top thread at the stitching zone. The parts will be returned to their rest positions, after a cutting operation, by the action of a tension spring anchored to the base of the machine and to the lever 37.

It will also be observed that the bar 20 of the first-described lever and linkage system is equipped with spaced collars 44 which are arranged to abut against the bearing collars 22. These collars 44 can be adjusted in position along the bar 20, thereby determining, in. one simple operation, the limits of the stroke of both cutting knives.

I claim:

ll. In a lockstitch sewing machine including a base plate, a stitch plate on said base plate, top thread supply means, bottom thread supply means and a presser foot arranged above the stitch plate, thread cutting equipment comprising a first cutter pivotally mounted on the presser foot above the stitch plate for action on the top thread, a second cutter pivotally mounted below the stitch plate for action on the bottom thread, first and second mechanical systems comprising interconnected levers and links connected to said first andsecond cutters respectively for operating the cutters independently of the mechanisms of the sewing machine, these mechanical systems being respectively disposed above and, below the base plate of the machine, coupling means connecting said systems together for simultaneous operation and extending through the base plate, a single manually-operable lever coupled to the coupling means and the mechanical systems for actuating the latter to implement pivotal movements of the cutters in performance of a thread-cutting operation and unitary adjustable limit means positioned on one of said mechanical systems adapted to control the stroke of the first and second cutters in common.

2. Thread cutting equipment as claimed in claim I, in which the mechanical system for operating the first cutter includes a lost-motion coupling permitting raising and lowering of the presser foot.

3. In a lockstitch sewing machine including a horizontal base plate, a stitch plate on said base plate, top thread supply means, bottom thread supply means and a presser foot arranged above the stitch plate, thread cutting equipment comprising a first cutter pivotally mounted on the presser foot above the stitch plate for action on the top thread, a second cutter pivotally mounted below the stitch plate for action on the bottom thread, first and second mechanical systems comprising interconnected levers and links connected to said first and second cutters respectively for operating the cutters independently of the mechanisms of the sewing machine, these mechanical systems being respectively disposed above and below the base plate of the machine, a stem mounted in the base plate ina vertical disposition extending through and rotatable with respect to said base plate, the upper end of the stem, above the base plate, being connected to the first mechanical system and the lower end of the stem, below the base plate, being connected to the second mechanical system, and a single manually-operated lever coupled to said rotatable stem and the mechanical systems for actuating the latter to implement pivotal movements of the cutters in performance of a thread cutting operation.

4. In a lockstitch sewing machine including a horizontal base plate, a stitch plate on said base plate, a cantilever arm, a stitching head carried by said arm, a presser foot on said stitching head above the stitch plate, top thread supply'means and bottom thread supply means, thread cutting equipment comprising a first cutter pivotally mounted on the presser foot for action on the top thread, a second cutter pivotally mounted below in the stitch plate for action on thebottom thread, first and second mechanical systems comprisinginterconnected levers and links connected to said first and second cutters respectively for operating the cutters independently of the mechanisms of the sewing machine, these mechanical systems being respectively disposed above and below the base plate of the machine, a lost-motion coupling in said first mechanical system permitting raising and lowering of the presser foot, adjustable limit means in one-of said mechanical systems controlling the stroke of both cutters in common, a stem mounted in-th'eba'se plate in a vertical disposition extending through said plate and in rotatable relation with respect to said plate, the upper end of this stem being connected to ,thefirst mechanical system and the lower end of the stem being connected to the second mechanical system, and a finger piece mounted on the cantilever arm of the machine andcoupled to said rotatable stem for turning the latter to operate the mechanical systems and implement pivotal movements of both cutters in performance ofa thread. cutting operation.

References Cited by the Examin er UNITED STATES PATENTS 5/1945 Chudner 112-252 5/1955 Artzt 112-252 

1. IN A LOCKSTITCH SEWING MACHINE INCLUDING A BASE PLATE, A STITCH PLATE ON SAID BASE PLATE, TOP THREAD SUPPLY MEANS, BOTTOM THREAD SUPPLY MEANS AND A PRESSER FOOT ARRANGED ABOVE THE STITCH PLATE, THREAD CUTTING EQUIPMENT COMPRISING A FIRST CUTTER PIVOTALLY MOUNTED ON THE PRESSER FOOT ABOVE THE STITCH PLATE FOR ACTION ON THE TOP THREAD, A SECOND CUTTER PIVOTALLY MOUNTED BELOW THE STITCH PLATE FOR ACTION ON THE BOTTOM THREAD, FIRST AND SECOND MECHANICAL SYSTEMS COMPRISING INTERCONNECTED LEVERS AND LINKS CONNECTED TO SAID FIRST AND SECOND CUTTERS RESPECTIVELY FOR OPERATING THE CUTTERS INDEPENDENTLY OF THE MECHANISMS OF THE SEWING MACHINE, THESE MECHANICAL SYSTEMS BEING RESPECTIVELY DISPOSED ABOVE AND BELOW THE BASE PLATE OF THE MACHINE, COUPLING MEANS CONNECTING SAID SYSTEMS TOGETHER FOR SIMULTANEOUS OPERATION AND EXTENDING THROUGH THE BASE PLATE, A SINGLE MANUALLY-OPERABLE LEVER COUPLED TO THE COUPLING MEANS AND THE MECHANICAL SYSTEMS FOR ACTUATING THE LATTER TO IMPLEMENT PIVOTAL MOVEMENTS OF THE CUTTERS IN PERFORMANCE OF A THREAD-CUTTING OPERATION AND UNITARY ADJUSTABLE LIMIT MEANS POSITIONED ON ONE OF SAID MECHANICAL SYSTEMS ADAPTED TO CONTROL THE STROKE OF THE FIRST AND SECOND CUTTERS IN COMMON. 